1. Field of the Invention
The present invention relates to protecting circuits from excessive in-rush (initial power-on) current and short circuits during a “hot swap” or when a short circuit is placed on a circuit output, and, more particularly, for providing such protection with few components and an efficient use of die area. “Hot swap” refers to inserting and removing a circuit into or out of a computer system, without removing or powering down the system. Short circuit protection ensures that the circuit will survive when a short, or zero ohms, is placed directly on the output to ground.
2. Background Information
In the past, power was disconnected while plugging and unplugging circuits into computer or other such electronic systems. This was necessary since the random making and breaking of contacts as a circuit board or module was being inserted or removed from a connector could harm the circuits and/or the system. The possible mis-connections to power, ground and signal inputs and outputs were not controlled. Shorting the output of a circuit may also inadvertently occur and be destructive.
However, the need to disconnect and later re-connect power is onerous, especially where entire systems may have to be powered down, possibly in set sequences, and later powering up, possibly in set sequences, and re-establishing conditions may take too much time. Moreover, any errors while powering down or up could create high currents and power glitches that may harm the circuits.
Power-on in-rush current limiting (protection) and short circuit protection may use the same criteria, but those skilled in the art may use different criteria.
Today, it is common to plug and unplug and plug circuits, memories, controllers, etc., into electronic systems without removing power. However, these hot swapping, short circuit protective circuits take up valuable die space in such systems and often must be located externally with respect to the system they are protecting.